Manufacture of synthetic spinels



stances hein all finely ture thus'o tained is a used in any of the 60known appliances, for instanceaccording to Patented June 13, 1933UNITED. STATES PATENT, OFFICE HERMAN)! ESPIG, OF BITTERFELD, GERMANY,ASSIGNOR TO G. FARBENINDUSTRIE AKTIENGESELLSGHAFT, OFFBANKFOBT-ON-THE-MA IN, GERMANY mmurao'runa or'srn'rnmrc srnmI-s NoDrawing. Application filed January 9, 1930, Serial No. 419,752, and inGermany February 11,

This invention relates toimprovements in the manufacture of syntheticspinels on the base of alumina and magnesia.

Synthetic spinels of this kind when produced according to a knownprocess, have a greenish-blue colour and the stones thus obtainedresemble in their appearance aquamarines and blue zircones. All thespinels when prepared in this manner however alter their appearance totheir disadvantage when viewed in artificial light inasmuch as theirbeautiful greenish-blue or sage-green colour changes into a greyishgreen, and lighter stones become almost colourless. Incontradistinction, the natural aquamarines and zircones show a morebeautiful lustre in artificial light than in the day light The object ofthe presentinvention is to remove this disadvantage of the known proc-'ess. This is effected by addin before the fusing process smallquantities o titanic acid,

say a out0.3 percent by weight, to the starting powdered mixture ofalumina and magnesia containin besides, the usual amounts of oxides of cromium, cobalt, vanadium either single or in combination for colouringpurposes. When viewed in day-light, the

additional content of titanic oxide does not perce tibly change thecolour of the stones resem ling aquamarines and zircones; but thediscolouration of the stones, otherwise occuring in artificial light,does in this case not take place and the stones then assume a vividgreenish-blue hue. I

Even when employin a starting mixture without any addition 0 the knowncolouring substances, the spinels obtained after the addition of titanicoxide alone ap marines, which colour, in artificial light, changes intoa bluish-green.

oxide, 0.025 parts of cobaltic oxide, said subowdered. The mixcar inablue hue resemblmgthe colour 0 aqua- Verneuils process, for obtainingsynthetic precious stones by means of an oxy-hydrogen low-pipe so as toproduce a raw bulb, ready to be cut and polished.

I claim: 1

1. A synthetic spinel having a permanent aquamarine colour consisting ofabout 92 parts of alumina, 8 parts of magnesia, 0.12 parts of chromicoxide, 0.025 parts of cobaltic oxide and 0.3 parts of titanic oxide.

2. A composition of matter'adapted to produce a synthetic spinel havinga permanent aquamarine colour, consisting of a basic mixture of about 92parts of alumina and about 8 parts of magnesia, and incorporated in saidbasic mixture approximately 0.12 parts of chromic oxide, 0.025 parts ofcobaltic oxide,

and 0.3 parts of titanic oxide. In testimony whereof, I afiix mysignature.

. HERMANN ESPIG.

